AP Macroeconomics

## Learning Outcomes

- Explain why a leftward shift of **SRAS** raises the price level and lowers real GDP
- Explain why a rightward shift of **SRAS** lowers the price level and raises real GDP
- Identify common causes of negative and positive supply shocks
- Distinguish between a shift of SRAS and a movement along the SRAS curve
- Use **LRAS** to classify recessionary and inflationary gaps after a supply shock
- Compare SRAS shocks with AD shocks in AP-style graph questions

## AP Macroeconomics Syllabus

For the AP Macroeconomics, you are expected to understand short-run changes in aggregate supply, with a focus on the following syllabus points:

- Know that a leftward shift of **SRAS** causes a higher price level and lower real GDP in the short run
- Know that a rightward shift of **SRAS** causes a lower price level and higher real GDP in the short run
- Identify common SRAS shifters, including nominal wages, input prices, productivity, and expected inflation
- Explain the difference between a change in the price level, which causes movement along SRAS, and a non-price change, which shifts SRAS
- Understand why a negative supply shock can create **stagflation**
- Use **LRAS** or potential output to identify a recessionary gap or inflationary gap after an SRAS shift
- Distinguish supply shocks from demand shocks by the direction of change in output and the price level

## Test Your Knowledge

_Attempt these questions before reading this article. If you find some difficult or cannot remember the answers, look more closely at that area during your revision._

1. What happens to the price level and real GDP when SRAS shifts left?
2. How is a negative supply shock different from a decrease in aggregate demand?
3. Name two events that could shift SRAS to the right.
4. Why can a recessionary gap exist at the same time as rising prices?
5. What is the difference between a movement along SRAS and a shift of SRAS?

## Introduction

In the AD–AS model, short-run aggregate supply shocks are one of the most tested reasons the economy can face a difficult mix of outcomes. When aggregate demand changes, price level and output usually move in the same direction. When **SRAS** changes, they move in opposite directions. That distinction is central on both multiple-choice questions and FRQs.

This topic matters because it explains why the economy can experience lower output and higher prices at the same time. That result is not possible from a simple demand decrease alone. On the AP exam, you must be able to identify the cause of the shift, show the graph result, and connect it to unemployment and gaps relative to potential output.

> **Key Term: short-run aggregate supply (SRAS)**
> The curve showing the relationship between the price level and the quantity of real GDP firms are willing to produce in the short run.

### Why SRAS slopes upward and why that matters

The SRAS curve slopes upward because, in the short run, some input costs are slow to adjust. If firms can sell their output at a higher price level while some costs, especially nominal wages, have not yet risen by the same amount, production becomes more profitable.

A useful AP way to think about this is through the **real wage**:

$$
\text{Real wage} \approx \frac{W}{P}
$$

where **W** is the nominal wage and **P** is the price level.

If the price level rises unexpectedly while nominal wages are sticky, then **W/P** falls. Labor becomes cheaper in real terms for firms, so they hire more workers and produce more output. That is movement upward along the SRAS curve, not a shift.

> **Key Term: sticky nominal wages**
> Wages that do not adjust immediately when the price level changes, helping explain why SRAS slopes upward.

This point is easy to miss. A higher current price level by itself does not shift SRAS. It causes a change in quantity of real GDP supplied along the existing SRAS curve.

That leads to a rule the AP exam tests often:

- If the variable on the vertical axis changes, there is movement along the curve
- If some other determinant changes, the whole SRAS curve shifts

So if the question says “the price level rises,” think movement along SRAS. If it says “oil prices rise” or “workers expect higher inflation,” think SRAS shift.

> **Test Tip:** If a question gives you a rise in wages, oil prices, or expected inflation, do not move along SRAS. Those are cost-side shifters, so the entire SRAS curve moves.

### What shifts SRAS left or right

SRAS shifts when firms’ per-unit production costs or productive efficiency change. A left shift means firms are willing to produce less at every price level. A right shift means firms are willing to produce more at every price level.

> **Key Term: negative supply shock**
> An event that raises production costs or disrupts production, shifting SRAS left.
>
> **Key Term: positive supply shock**
> An event that lowers production costs or improves productive efficiency, shifting SRAS right.

Common causes of a leftward SRAS shift include:

- higher nominal wages
- higher oil or energy prices
- higher imported input prices
- lower productivity
- higher expected inflation
- destruction of productive capacity from a natural disaster

Common causes of a rightward SRAS shift include:

- lower nominal wages
- lower input or energy prices
- improved productivity
- lower expected inflation
- favorable supply conditions that reduce production costs

The logic must always run from **cause to cost to curve shift to macro result**.

For example, suppose oil prices rise sharply. Oil is an input for transport, plastics, chemicals, shipping, and manufacturing. Higher oil prices raise firms’ costs across much of the economy. Since production is now less profitable at every price level, SRAS shifts left. The new equilibrium has a higher price level and lower real GDP.

Notice what is cause and what is effect:

- Higher oil prices are the cause
- Leftward SRAS shift is the graph change
- Higher price level and lower output are the effects

Students often reverse this and say “higher prices cause SRAS to shift left.” That is imprecise. Here, higher input costs cause SRAS to shift left; the higher overall price level comes after the shift.

A productivity example works the other way. Suppose new software lets shipping firms route deliveries more efficiently and factories waste fewer materials. Unit costs fall. Firms can profitably produce more at each price level, so SRAS shifts right. The result is lower price level and higher real GDP.

### Reading the graph: output, prices, unemployment, and gaps

When SRAS shifts left with AD unchanged, the short-run equilibrium moves up and left. That means:

- **price level rises**
- **real GDP falls**
- **unemployment rises**

When SRAS shifts right with AD unchanged, the equilibrium moves down and right. That means:

- **price level falls**
- **real GDP rises**
- **unemployment falls**

These opposite movements are the signature of an SRAS shock.

> **Key Term: stagflation**
> A situation with rising prices, falling real GDP, and rising unemployment, usually caused by a leftward shift of SRAS.

Stagflation is especially testable because it feels unusual. Normally students connect recession with falling prices or inflation with strong output. A negative supply shock breaks that pattern. Output falls because production becomes more costly, but prices rise because the fall in supply pushes the equilibrium price level upward.

Use **LRAS** to classify the gap. If the new equilibrium real GDP is to the left of potential output, the economy has a recessionary gap even though the price level is higher.

> **Key Term: recessionary gap**
> A situation in which equilibrium real GDP is below potential output, so unemployment rises above the natural rate.

A leftward SRAS shift can therefore create both:

- inflation, because the price level rises
- a recessionary gap, because output falls below potential

That is exactly why stagflation is so troublesome for policy makers.

A rightward SRAS shift can push real GDP above potential output in the short run if the economy begins at full-employment output and supply conditions improve suddenly. In that case unemployment falls below the natural rate and there may be an inflationary gap in reverse logic, though for this subtopic the more common AP focus is lower prices and higher output.

### SRAS shocks versus AD shocks

Many AP errors come from mixing up supply and demand changes. The quickest distinction is this:

- **AD shocks:** price level and real GDP move in the same direction
- **SRAS shocks:** price level and real GDP move in opposite directions

Here is the comparison students need:

| Shock             | Price level | Real GDP |
| ----------------- | ----------: | -------: |
| AD shifts left    |        down |     down |
| AD shifts right   |          up |       up |
| SRAS shifts left  |          up |     down |
| SRAS shifts right |        down |       up |

If you see a scenario where output falls and prices rise, the answer is not a drop in AD. It must be a leftward SRAS shift.

Worked example:

Suppose a hurricane destroys ports, warehouses, and some factory equipment. What happens in the short run?

Step 1: Identify the side of the model affected.  
This is a production disruption, so it affects supply, not demand.

Step 2: Decide direction.  
Destroyed capital and disrupted logistics reduce productive capacity in the short run, so **SRAS shifts left**.

Step 3: Read the new equilibrium.  
With AD unchanged, equilibrium moves up and left.

Step 4: State macro results.  
Price level rises, real GDP falls, unemployment rises.

> **Answer:** A hurricane that disrupts production is a negative supply shock. SRAS shifts left, causing a higher price level and lower real GDP in the short run.

Another worked example:

Suppose nominal wages fall while aggregate demand is unchanged.

Step 1: Lower wages reduce firms’ production costs.  
Step 2: Lower costs make firms willing to produce more at every price level.  
Step 3: SRAS shifts right.  
Step 4: Equilibrium price level falls and real GDP rises.

> **Answer:** Lower nominal wages shift SRAS right, reducing the price level and increasing real GDP in the short run.
>
> **Test Tip:** In FRQs, write the chain clearly: “input costs rise → SRAS shifts left → price level rises and real GDP falls.” That kind of step-by-step explanation earns points more reliably than a short final statement.

### Common AP traps and how to avoid them

First, do not confuse a change in the current price level with a change in expected inflation. A rise in the current price level causes movement along SRAS. A rise in expected inflation shifts SRAS left because firms expect higher future costs or may delay supplying now.

Second, do not say a rise in wages increases SRAS. Higher wages raise costs, so SRAS decreases and shifts left.

Third, do not forget unemployment. The graph may only show price level and real GDP, but AP questions often ask for labor-market consequences too. Lower output means firms need fewer workers, so unemployment rises after a leftward SRAS shift.

Fourth, do not confuse SRAS with LRAS. A temporary oil-price spike is mainly an SRAS issue in this topic. LRAS changes only when the economy’s long-run productive capacity changes, such as from sustained changes in resources or technology.

Finally, use exact graph language. The vertical axis is **price level** and the horizontal axis is **real GDP/output**. On FRQs, label curves **AD**, **SRAS**, and when needed **LRAS**.

## Key Point Checklist

_This article has covered the following key knowledge points:_

- SRAS shocks change output and the price level in opposite directions
- A leftward SRAS shift raises the price level and lowers real GDP
- A rightward SRAS shift lowers the price level and raises real GDP
- Negative supply shocks include higher nominal wages, higher oil prices, lower productivity, and supply disruptions
- Positive supply shocks include lower input costs, better productivity, and lower expected inflation
- A change in the current price level causes movement along SRAS, not a shift
- Sticky nominal wages help explain why SRAS slopes upward
- A negative supply shock can create stagflation: higher prices, lower output, and higher unemployment
- A leftward SRAS shift can create a recessionary gap if output falls below LRAS or potential output
- AD shocks move price level and output in the same direction, while SRAS shocks move them in opposite directions
- On AP graphs, the vertical axis is price level and the horizontal axis is real GDP or output
- Clear cause-and-effect chains are essential for FRQ explanations

## Key Terms and Concepts

- short-run aggregate supply (SRAS)
- sticky nominal wages
- negative supply shock
- positive supply shock
- stagflation
- recessionary gap


Changes in the AD–AS Model in the Short Run - SRAS shocks affect output and prices